1. Field of the Invention
The present invention relates generally to electrodes for sensing the electrical potential of a person's skin and, more particularly, is concerned with an electrode having a removable nonconductive plastic abrading brush and with a method and apparatus for assembling the same.
2. Description of the Prior Art
Electroencephalograms (EEG) and electrocardiograms (EKG) are commonly performed on medical patients by sensing the electrical potential of skin covering the brain and heart, respectively. The skin potential is sensed by use of conductive elements called probes, monitors or electrodes. One or more electrodes are placed in electrical contact with the blood-rich epidermis layer of skin.
One standard electrode used is composed of silver metal and takes the form of a hollow, frusto-conical shaped disc. The disc-shaped electrode defines an open cavity for receiving an electrolyte cream. A hole is provided in the electrode for injecting a supplemental quantity of the electrolyte cream into the cavity if needed. A conductor is attached to the electrode and the electrolyte cream provides a conductive coupling between the skin and the electrode.
The standard electrode is not self-preparing, that is, it cannot be used just by being place against the person's skin. Instead, before the electrode is applied to the person's skin, the location on the skin where it will be applied must be prepared by shaving the hair so that then the skin can be abraded with an abrading tool or an abrading grit-bearing electrolyte cream to remove the outer dead skin layer and facilitate making electrical contact by the electrode with the blood-rich epidermis skin layer.
In medical applications which are typically carried out by skilled personnel, the shaving and abrading procedures can be performed rather quickly. Increasingly, EEG measurements also have non-medical applications. However, in non-medical applications EEG measurements are typically carried out by unskilled personnel. The above-outlined skin preparation procedures are time-consuming and generally unacceptable for persons involved in non-medical applications.
Recently, an electrode incorporating a conductive brush has been devised which is characterized as self-preparing. It is disclosed in U.S. Pat. No. 4,706,679 to Schmidt et al which is assigned to the same assignee as the present invention. Its use does not require shaving of the hair from the skin at the location where the electrode is to be applied. Abrading is accomplished by the tips of the bristles of the brush which when pressed against the skin penetrate or abrade through the dead layer of skin. The conductive brush bristles or strands being composed of silver metal maintain electrical contact with the skin. This conductive brush electrode can be applied in a few seconds compared to fifteen to thirty minutes for the standard electrode.
However, problems have been encountered in the use of this conductive brush electrode in measurement of transient evoked potentials. Steady state fields develop around the conductive bristles or strands. Ion concentrations develop near the end or tip points of the brush strands causing interference with measurements.
Consequently, a need exists for another approach to providing a self-preparing electrode which will overcome the problems encountered with the recent conductive brush electrode without returning to the earlier time-consuming preparation procedures.